T-Shirt Fabric Guide: Cotton, Blends, and Weight

Two T-shirts can look identical on a rack and feel nothing alike after a month of wear. The difference lives in the fiber, the way it was spun into yarn, the knit, and the weight of the fabric. Most of that is printed on the label or the product page if you know what the words mean, and this guide walks through each one.

Cotton: what the label words mean

"100% cotton" tells you the fiber, not the quality. Two steps that happen before the fabric is ever knitted, combing and spinning, make a large difference, and both show up on labels.

Combed cotton

Cotton headed for yarn is carded first, a brushing step that opens the fibers, lines them up roughly parallel and removes some trash. Combing is an optional extra step on top of that. According to a Cotton Incorporated technical bulletin on spun yarns, combing removes short fibers, neps (small tangles of fiber) and trash particles while laying the remaining fibers parallel. The bulletin says this can significantly improve a yarn's uniformity, softness, strength and luster, and that combed yarns shed less lint later on.

Ring-spun and open-end yarn

Spinning twists fibers into yarn, and the two methods you will see mentioned most on tees are ring spinning and open-end spinning, also called rotor spinning. The same Cotton Incorporated bulletin compares them directly. Ring-spun yarn comes out as the strongest, finest and softest of the common types, and also the slowest and most expensive to produce. Open-end yarn is more even, faster and cheaper to make, with a harsher feel and less strength.

That is why "combed ring-spun cotton" shows up on so many better tees. It pairs the cleaner fiber from combing with the softer yarn from ring spinning. Neither phrase guarantees a great shirt, but a tee that lists both started from better yarn than one that lists neither.

Pima and Supima

Fiber length is the other big variable. The Supima organization's FAQ says the most common cotton grown around the world has a fiber length of only about 1 inch, while Supima fiber averages 1.5 inches. Shorter fibers make yarn that is rougher and more prone to pilling; longer fibers make fabric that is stronger, softer and better at resisting pills over time.

The two names get used as if they were the same, but they are not:

• Pima. The Supima FAQ notes that at retail, "Pima" has become a generic term for better cotton, and that it does not necessarily mean the shirt was made with extra-long staple fiber.
• Supima. This is a trademark for American-grown, extra-long staple cotton. According to the organization, it is grown only in California, Arizona, Texas and New Mexico, it makes up less than 1% of the cotton grown in the world, and products must be sourced through a licensed supply chain to carry the name.

The practical reading: "Pima" on a label is a hint, while "Supima" is a licensed name tied to a specific fiber and origin.

Blends: polyester, tri-blend and modal

Blends trade some of cotton's qualities for others. The fiber content label lists each fiber with its percentage, so that is the first place to look.

Polyester. A synthetic fiber, and a thermoplastic one. Cotton Incorporated's guide to shrinkage in cotton fabrics points out that thermoplastic synthetics can be heat set for stability and do not swell and deswell with water the way cotton does. In other words, the polyester share of a blend is more dimensionally stable than the cotton share. Polyester also changes the hand (the feel) and the drape, so try a blend on before buying several.

Tri-blend. The term usually means three fibers, typically cotton, polyester and rayon. The proportions vary by maker, so read the label rather than assuming a recipe.

Modal. European Union textile rules define modal as a regenerated cellulose fiber made by a modified viscose process, with a high breaking force and a high wet modulus. In plain terms, it starts from cellulose like viscose rayon does, but it is engineered to be stronger and to resist stretching out of shape when wet.

Jersey: the knit behind most tees

Woven fabrics interlace yarns at right angles. T-shirts are knitted instead, and CottonWorks, a Cotton Incorporated resource, calls single jersey the most common knit fabric, found in T-shirts, underwear and swimwear.

What that means for your shirt:

• Two different sides. The technical face shows vertical columns of stitches; the back shows horizontal rows. That is why the outside of a tee looks smooth and the inside looks faintly ridged.
• More stretch across than down. CottonWorks says jersey stretches roughly twice as much across its width as along its length, one reason a tee gives around the chest but keeps its length.
• Edges curl. Cut jersey curls at the edge and can run, one reason tee edges are usually hemmed or bound.

The same page describes two double knits. Rib looks the same on both sides and stretches about twice as far across as single jersey. Interlock, made by combining two rib fabrics, also looks the same on both sides and is very stable, with no curling.

Fabric weight, in ounces per square yard

Fabric weight is the weight of one square yard of the fabric, stated in ounces. The figure describes the cloth, not the finished shirt, so a large tee and a small tee cut from the same fabric share the same number.

What the number tells you:

• Higher numbers mean more fiber in each square yard. Heavier jersey is generally more opaque, holds its shape better and hangs straighter.
• Lower numbers mean lighter fabric that generally drapes more and feels cooler, at the cost of more see-through and more cling.

Makers use words like "lightweight" and "heavyweight," but they draw those lines in different places, so compare the numbers themselves. Compare like with like as well: a cotton and polyester blend can feel quite different from all-cotton jersey of the same weight.

Check the unit, too. Some mills quote ounces per linear yard, which as Fashion-Incubator explains is one yard of length at whatever width the roll happens to be, so the number depends on the roll width and cannot be compared with a per-square-yard figure. If a listing gives no unit, look for "oz/sq yd" on the specification sheet before relying on the figure.

Why cotton tees shrink

Cotton knits shrink for a specific reason. Cotton Incorporated's shrinkage guide explains that knits are very sensitive to the pulling and stretching they get during processing, and that some of that stretch remains in the fabric as residual shrinkage waiting to be released. Water and drying release it. As a knit dries, its loops try to return to a rounder, relaxed shape, and the fabric gets shorter.

Two findings from that guide are especially useful at home:

• Tumbling releases it all. If a garment is tumble dried, the guide says, all of its available residual shrinkage will be realized. Line drying or drying flat leaves much of it in place.
• Heat level was not the driver in their test. Cotton Incorporated tumble dried a 100% cotton interlock at 100°F, 150°F and 200°F and got identical shrinkage curves at all three temperatures. Most of the drying shrinkage happened late, once the fabric's moisture content fell below about 20%.

The practical takeaway: if you want a cotton tee to stay its current size, skip the dryer or pull the shirt out while it is still damp and let it finish flat. Mills can also reduce residual shrinkage during finishing with relaxation drying and compaction, one reason some tees shrink noticeably less than others.

Reading the care label

In the US, the FTC's Care Labeling Rule defines the words on the label. Its glossary sets the washing temperatures by initial water temperature:

The same glossary says "tumble dry" with no temperature means a hot dryer setting may be used regularly, "line dry" means hanging the item damp from a line or bar, and "dry flat" means laying it out horizontally. The label tells you what the garment can survive. If you want less shrinkage than the label allows, choose the gentler option it lists or line dry.

A quick checklist when you shop

• Look for combed and ring-spun on all-cotton tees.
• Treat Pima as a hint and Supima as a licensed name for a specific American cotton.
• Read the fiber percentages on any blend, and remember that tri-blend recipes vary.
• Compare ounces per square yard instead of words like "heavyweight."
• Plan on line drying a cotton tee you want to keep at its current size.

The label will not tell you everything, but these five checks rule out most of the shirts that disappoint after a few washes.